In the first figure you can see 2 shells together encasing the plug. In the second figure you can see the plug with the shells removed. The shells is where the body is laid up upon.

The shells here are pushed together and covered with a felt material to soften the sharp edges on the exterior of the mold. These sharp edges could possibly puncture the vacuum bag that will later be put over the mold.

The mold is covered in 2 layers of fiber glass fit precisely throughout the mold. A layer of a silk type material is then laid over top of this. It helps the resin soak through. Another layer of a mesh (red) is laid out to leave space for the resin to flow throughout the mold. All the seams are sealed with felt and spray on adhesive. The edges of the mold are all taped up.

Hoses are laid out along specific areas of the mold. A bag is raped around the mold and sealed. Notice the hoses are not a continuous closed tube, this way resin can flow out at different areas of the tube. Sealed hoses are then attached outside the bag to a vacuum pump that sucks air out of the bag. That black circular object is a resin trap for excess resin  that happened to flow through the mold. It will prevent resin from flowing into the pump.

Each resin hose is attached to a sealed hose outside the bag. Each sealed hose is clamed to prevent air from being sucked into the bag and keep a relatively high vacuum. Once the pump is turned on, one hose at a time is unclamped and put into a bucked of resin. The resin flows through the tubes and into the part. You can see in the figure above at the bottom left, resin leaking into the fiberglass. Air is sucked from the rear of the part while resin enters at the front of the part.

The bag is then taken off the part when the resin is in a gel state. That way it is easier to remove the bag and layers of felt. The finished part will be stronger and lighter then with doing a wet laid up process.